Lipid layers, such as comprise cell membranes and the extracellular matrix of the stratum corneum, can constitute a formidable barrier to drug delivery. For optimal delivery, a drug should freely dissolve in both the aqueous compartments of the body and the lipid layers which enclose those compartments.
Although many low-molecular-weight compounds of low to moderate polarity can pass directly through lipid layers, compounds with greater polarity and/or higher molecular weight generally enter eukaryotic cells only via endocytosis or related processes. In this process, compounds are taken into the cell via progressive invagination of a region of the membrane, eventually forming a closed vesicle, or endosome, within the cell. In most cases, the endosome then merges with a lysosome, resulting in exposure of the internalized compound to degradative enzymes.
To facilitate more effective delivery of drugs and other compounds across lipid layers, it would be desirable to provide a drug transporting composition which affords lipid solubility under selected conditions and aqueous solubility under other conditions. It would also be desirable to deliver compounds into the cell cytosol via a route which avoids exposure to lysosomal enzymes.